[CodeGen] Make __clang_call_terminate have an unwind table entry

This enables unwinders to step past that frame on architectures that
don't use DWARF unwinding (such as armv7), e.g. when debugging. The
problem should theoretically be architecture-agnostic, but according to
https://discourse.llvm.org/t/51633/2 it gets masked on architectures
that use DWARF unwind info.

Fixes #40696

Reviewed By: efriedma, rnk

Differential Revision: https://reviews.llvm.org/D151393

Author: smeenai

clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -4689,6 +4689,7 @@ static llvm::FunctionCallee getClangCallTerminateFn(CodeGenModule &CGM) {
       cast<llvm::Function>(fnRef.getCallee()->stripPointerCasts());
   if (fn->empty()) {
     CGM.SetLLVMFunctionAttributes(GlobalDecl(), FI, fn, /*IsThunk=*/false);
+    CGM.SetLLVMFunctionAttributesForDefinition(nullptr, fn);
     fn->setDoesNotThrow();
     fn->setDoesNotReturn();
 

clang/test/CodeGenCXX/clang-call-terminate.uwtable.cpp

@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fexceptions -fcxx-exceptions -emit-llvm -o - %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,NOUNWIND %s
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fexceptions -fcxx-exceptions -funwind-tables=1 -emit-llvm -o - %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,SYNCUNWIND %s
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -fexceptions -fcxx-exceptions -funwind-tables=2 -emit-llvm -o - %s | \
+// RUN:   FileCheck --check-prefixes=CHECK,ASYNCUNWIND %s
+
+void caller(void callback()) noexcept { callback(); }
+
+// CHECK: define {{.*}}void @__clang_call_terminate({{[^)]*}}) #[[#ATTRNUM:]]
+// CHECK: attributes #[[#ATTRNUM]] = {
+// NOUNWIND-NOT: uwtable
+// NOUNWIND-SAME: }
+// SYNCUNWIND-SAME: uwtable(sync)
+// ASYNCUNWIND-SAME: uwtable{{ }}